1Sift flour and salt together into large bowl. Using two knives or a pastry blender, cut in cubes of shortening until mixture resembles small peas. Make a well in centre of ingredients. Combine egg yolk, vinegar and water. Pour into well and mix in thoroughly with a knife. Beat egg white until soft peaks form, then fold into dough. Knead briefly on a floured surface. Press dough into a ball and wrap well. For best results, freeze, then thaw in refrigerator. Roll out into desired shapes. Makes enough for four eight-inch(20-cm) double-crust pies.